SIMULATION EXPERIMENT OF BIOGENIC GAS FROM SOURCE ROCK AND BIODEGRADATION OF CRUDE OIL IN THE JIYANG DEPRESSION, THE BOHAI BAY BASIN

Detection of the bacteria in the source rocks from different types of formation,lithology and depth in the Jiyang Depression was carried out in this paper.The result shows that the methane-forming bacteria exist in mudstone and sandstone in Es³,Es¹ and Ed formations with depth being from 1 297 to 2 522 meters,indicating that the existence of methane-forming bacteria depends on the survival environment of the bacteria and is independent of rock's formation and lithology.The characteristics of the biogenic gases from source rocks and biodegradation of crude oil are similar in simulation experiment.The products of simulation experiment are mathane and carbon dioxide.Temperatures at the biogenic gas generating peak are 45℃ and 65℃.The yields of biogenic gases generated by a ton of TOC and a ton of crude oil are 20-160 m³ and 10-15 m³ respectively.Carbon isotope compositions of methane which range between -80.2‰ and -41.5‰ become lighter with simulation temperature going up,while carbon isotope compositions of carbon dioxide become heavier.Hydrogen isotope compositions of biogenic gas in simulation which mainly range between -300‰ and -350‰ are lighter than those in actual formation like the Luliang Basin in Yunnan Province which mainly range between -240‰ and -270‰.